Magnesium hydride has attracted great attention because of its high theoretical capacity and outstanding reversibility, nevertheless, its practical applications have been restricted by the disadvantages of the sluggish kinetics and high thermodynamic stability. In this work, an unexpected high reversible hydrogen capacity over 8.0 wt% has been achieved from MgH₂ metal hydride composited with small amounts of LiBH₄ and Li₃AlH₆ complex hydrides, which begins to release hydrogen at 276°C and then completely dehydrogenates at 360°C. The dehydrogenated MgH₂+LiBH₄/Li₃AlH₆ composite can fully reabsorb hydrogen below 300°C with an excellent cycling stability. The composite exhibits a significant reduction of dehydrogenation activation energy from 279.7 kJ/mol (primitive MgH₂) to 139.3 kJ/mol (MgH₂+LiBH₄/Li₃AlH₆), as well as a remarkable reduction of dehydrogenation enthalpy change from 75.1 kJ/mol H₂ (primitive MgH₂) to 62.8 kJ/mol H₂ (MgH₂+LiBH₄/Li₃AlH₆). The additives of LiBH₄ and Li₃AlH₆ not only enhance the cycling hydrogen capacity, but also simultaneously improve the reversible de/rehydrogenation kinetics, as well as the dehydrogenation thermodynamics. This notable improvement on the hydrogen absorption/desorption behaviors of the MgH₂+LiBH₄/Li₃AlH₆ composite could be attributed to the dehydrogenated products including Li₃Mg₇, Mg₁₇Al₁₂ and MgAlB₄, which play a key role on reducing the dehydrogenation activation energy and increasing diffusion rate of hydrogen. Meanwhile, the LiBH₄ and Li₃AlH₆ effectively destabilize MgH₂ with a remarkable reduction on dehydrogenation enthalpy change in terms of thermodynamics. In particular, the Li₃Mg₇, Mg₁₇Al₁₂ and MgAlB₄ phases can reversibly transform into MgH₂, Li₃AlH₆ and LiBH₄ after rehydrogenation, which contribute to maintain a high cycling capacity. This constructing strategy can further promote the development of high reversible capacity Mg-based materials with suitable de/rehydrogenation properties.

氢化镁由于其较高的理论容量和出色的可逆性而备受关注，尽管如此，其实际应用受到动力学反应迟钝和热力学稳定性高的缺点的限制。在这项工作中，由MgH ₂金属氢化物与少量LiBH ₄和Li ₃ AlH ₆复合氢化物复合获得了意想不到的高可逆氢容量，超过8.0 wt％，该金属氢化物在276开始释放氢。°C，然后在360°C完全脱氢℃。脱氢的MgH ₂ + LiBH ₄ / Li ₃ AlH ₆复合材料可充分吸收300以下的氢°C具有出色的循环稳定性。该复合材料的脱氢活化能从279.7 kJ / mol（原始MgH ₂）显着降低至139.3 kJ / mol（MgH ₂ + LiBH ₄ / Li ₃ AlH ₆），脱氢焓变从75.1显着降低kJ / mol H ₂（原始MgH ₂）至62.8 kJ / mol H ₂（MgH ₂ + LiBH ₄ / Li ₃ AlH ₆）。LiBH ₄和Li ₃ AlH ₆的添加剂不仅提高了循环氢的容量，而且同时提高了可逆的脱氢/重氢动力学，以及脱氢热力学。MgH ₂ + LiBH ₄ / Li ₃ AlH ₆复合材料的氢吸收/解吸行为的显着改善可归因于包括Li ₃ Mg ₇，Mg ₁₇ Al ₁₂和MgAlB ₄在内的脱氢产物。降低了脱氢活化能，提高了氢的扩散速度。同时，LiBH ₄和Li ₃ AlH ₆有效降低MgH _2的稳定性，并从热力学角度显着降低脱氢焓的变化。特别地，Li ₃ Mg ₇，Mg ₁₇ Al ₁₂和MgAlB ₄相在重新氢化后可以可逆地转化为MgH ₂，Li ₃ AlH ₆和LiBH ₄，这有助于维持高循环容量。这种构造策略可以进一步促进具有合适的脱氢/再氢化性能的高可逆容量镁基材料的开发。